1. Field of the Invention
The present invention relates to a processing apparatus and a processing apparatus maintenance method.
2. Description of Related Art
Various types of processing apparatuses including a plasma etching apparatus are used in the manufacturing of semiconductor devices or LCD substrates in the related art. The plasma etching apparatus, for instance, etches a workpiece such as a semiconductor wafer or a glass substrate placed on an electrode (a lower electrode) with plasma generated from a specific type of process gas inside a vacuum-processing chamber. During the etching process, the temperature of the workpiece is maintained at a specific level so as to ensure that the temperature of the workpiece is not raised by the plasma, to improve the etching aspect ratio and to regulate the shape of the etched workpiece.
The temperature of the workpiece is normally controlled by a cooling mechanism disposed at the electrode. Such a cooling mechanism adopts a structure in which a primary coolant (e.g., brine) is supplied into a coolant circulating path running inside the stage and the workpiece is cooled as the primary coolant absorbs heat. The temperature of the primary coolant is controlled at a freezing circuit through which a secondary coolant (e.g., Freon) circulates. The primary coolant in a coolant tank, the temperature of which has been controlled at the freezing circuit, is supplied into the coolant circulating path with a pump, and the temperature of the primary coolant returning from the coolant circulating path is adjusted again at the freezing circuit before the primary coolant is stored into the coolant tank. The drive of the freezing circuit is controlled so as to maintain the temperature of the primary coolant at a predetermined level by monitoring the temperature of the primary coolant inside the coolant tank or the temperature of the primary coolant supplied from the coolant tank into the coolant-circulating path.
Examples of multiple freezing cycles achieved by combining a primary coolant circulating circuit and a secondary coolant circulating circuit include that disclosed in Japanese Laid Open Patent Publication No. H08-203866.
The cooling mechanism in the processing apparatus adopting the structure described above requires two circuits, i.e., a primary coolant circulating circuit constituted with a coolant tank, a pump and the like and a freezing circuit (a secondary coolant circulating circuit) constituted with a compressor, a condenser, an expansion valve and an evaporator, and thus a problem arises in that the apparatus requires a significant installation area. In addition, there is another problem in that since heat is exchanged multiple times between the workpiece and the primary coolant, between the primary coolant and the secondary coolant, and between the secondary coolant and the atmosphere in the structure having the two circuits, the extent of energy loss is bound to be significant.
Furthermore, in the cooling mechanism in the processing apparatus adopting the structure described above, brine and Freon, for instance, are used respectively as the primary coolant and the secondary coolant. These PFC (perfluorocarbon) gases have high GWP (global warming potential) values and significantly hasten the process of global warming. From the viewpoint of global environment protection, it is crucial to minimize the use of PFC gases.